Installation of iOS <9.x on A1460 iPAD 3

Hello

I am a little bit lost ... I would like to install iOS 6, 7 or 8 to an iPAD 3 (model A1460). This model is described as "shipped with iOS 6" but I cannot install iOS less 9.1 to it.

I found a website which says this model does only accept iOS 9.x, but also 9.0, 9.0.1, 9.0.2 installation does not work (I am booting the iPAD to maintenance mode and try to install via iTunes, forcing selection of ipsw file via ALT key).

I am wondering, as the iPAD is from 2014, where no iOS 9.x was available AFAIK.

Is the usage of the shift key different in its effect from the option (alt) key? I already tried to install ipsw by using option key (which enables selection of ipsw), but if I try to install anything below 9.1 it says that the iPad is not compatible with that version - and I am wondering, as I said, as this version of iPad was shipped with iOS6 in the beginning.

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